The present invention concerns methods for the synthesis of pyridine-based compounds, which compounds are useful as intermediates for the manufacture of pharmaceutical compounds.
Over the past three decades a large variety of antibiotics have become available for clinical use. Unfortunately, the wide-spread use of these antibiotics has caused a rapid increase in the number of bacterial strains that are resistant to the currently available antibiotics.
S. Hecker et al., PCT Application WO 01/21623 (published Mar. 29, 2001), describes 7-acylamino-3-heteroarylthio-3-cephem carboxylic acid antibiotics and prodrugs thereof. The compounds described therein are active as antibiotics against a wide spectrum of organisms including organisms which are resistant to beta-lactam antibiotics. However, the compounds described therein are complicated, and require the synthesis of a variety of separate groups. One group which must be synthesized to make these compounds is the C3 side-chain, an intermediate for which is illustrated on page 51 therein as follows: 
However, the synthesis of such C3 side chain groups as set forth in S. Hecker et al. requires in excess of 6 steps (see pages 49-52 therein). Accordingly, there is a need for new ways to make the intermediates used to make the antibiotic compounds described in S. Hecker et al.
Accordingly, a first aspect of the present invention is a method of making a compound of Formula VI: 
wherein:
Tr is a triphenyl group;
R1, R2 and R3 are each independently selected from the group consisting of H, C1-C4 alkyl, C1-C4 alkoxy, aryl, heteroaryl, and arylalkyl;
R4 is C2-C6 alkyl, and
R5 and R6 are each independently H or C1-C4 alkyl,
comprising:
reacting a compound of Formula V: 
with Tr-OH to produce a compound of Formula VI.
A second aspect of the present invention is a method of making a compound of Formula V as described above, the method comprising reacting a compound of Formula IV: 
where tBu is tert-Butyl or other suitable leaving group, with R6R5NR4SSR4NR5R6 in the presence of a strong amide base to produce a compound of Formula V.
A third aspect of the present invention is a method of a compound of Formula IV as described above, comprising reacting a compound of Formula III: 
wherein X is halogen, with sodium tert-butylthiolate or potassium tert-butylthiolate to produce a compound of Formula IV.
A fourth aspect of the present invention is a compound of Formula VI: 
wherein:
Tr is a triphenyl group;
R1, R2 and R3 are each independently selected from the group consisting of H, C1-C4 alkyl, C1-C4 alkoxy, aryl, heteroaryl, and arylalkyl;
R4 is C2-C6 alkyl, and
R5 and R6 are each independently H or C1-C4 alkyl;
subject to the proviso that (i) R1, R2 and R3 are not all simultaneously H, or (ii) R4 is not C2, or (iii) R5 and R6 are not simultaneously H.
A further aspect of the present invention is a compound of Formula V: 
wherein:
tBu is tert-butyl, or other suitable leaving group;
R1, R2 and R3 are each independently selected from the group consisting of H, C1-C4 alkyl, C1-C4 alkoxy, aryl, heteroaryl, and arylalkyl;
R4 is C2-C6 alkyl, and
R5 and R6 are each independently H or C1-C4 alkyl.
Compounds of Formula VI above are useful as intermediates in the manufacture of antibiotic compounds.
Compounds of Formula V above are useful as intermediates in the manufacture of compounds of Formula VI.
The foregoing and other objects and aspects of the present invention are explained in greater detail in the specification set forth below.
xe2x80x9cAlkylxe2x80x9d as used herein refers to linear or branched alkyl, preferably linear alkyl, including but not limited to methyl, ethyl, propyl, and butyl (Bu).
xe2x80x9cHaloxe2x80x9d as used herein refers to any suitable halogen group, such as fluoro, chloro, bromo, or iodo.
xe2x80x9cArylxe2x80x9d as used herein refers to any suitable aromatic group, such as phenyl, which aromatic group may be substituted or unsubstituted.
xe2x80x9cArylalkylxe2x80x9d as used herein refers to any suitable aryl group covalently coupled to an alkyl group, such as benzyl.
xe2x80x9cTriphenylxe2x80x9d or xe2x80x9cTrxe2x80x9d groups as used herein may be unsubstituted or substituted one or more times by additional groups such as C1-C4 alkyl, C1-C4 alkyloxy, or halo. Para substitutions are preferred, but substitutions may be of any number from 1 to 5 and in any position, with mono or di substitutions preferred.
As noted above, a first aspect of the present invention is a method of making a compound of Formula VI: 
wherein:
Tr is a triphenyl group;
R1, R2 and R3 are each independently H C1-C4 alkyl, C1-C4 alkoxy, aryl, heteroaryl, or arylalkyl (preferably H),
R4 is C2-C6 alkyl (preferably C2), and
R5 and R6 are each independently H or C1-C4 alkyl (preferably H).
The method comprises reacting a compound of Formula V: 
with Tr-OH to produce a compound of Formula VI. The reacting step is may be carried out as a one-pot, two step reacting step. The reaction step is preferably carried out in the presence of a strong organic acid, examples including but not limited to methanesulfonic acid and arylsulfonic acid (e.g., paratoluene sulfonic acid). The reacting step is typically carried out in a polar solvent such as acetic acid, which solvent is preferably non-aqueous, and may be carried out at any suitable temperature such as at room temperature.
Compounds of Formula VI are useful, among other things, as C-3 side chain intermediates useful for the production of 7-acylamino-3-heterarylthio-3-cephem carboxylic acid antibiotics, and prodrugs thereof, as shown in S. Hecker et al., PCT Application WO 01/21623 (Mar. 29, 2001) (see pages 49-50). Particularly organisms for which the compounds of the invention may be used as antibiotics include but are not limited to Staphylococcus aureus, Enterobacteriaceae, and Pseudomonas. The compounds may be used in vivo as a pharmaceutical agent by (for example), oral, parenteral, or topical administration, or may be used in vitro, for example as a topical or surface antibiotic.
A compound of Formula V above may be produced by reacting a compound of Formula IV: 
with R6R5NR4SSR4NR5R6 (which may be produced in accordance with known techniques), preferably in the presence of a strong amide base, to produce a compound of Formula V. This reacting step may be carried out in any suitable solvent, typically an etherial solvent such as dialkyl ether (e.g., diethyl ether), dimethoxyethane, tetrahydrofuran, or mixtures thereof. Any suitable strong amide base may be used, such as lithium, sodium, and potassium amide bases. Any suitable amide may be used, such as a dialkyl amide (e.g, diethyl amide). The temperature at which the reacting step is carried out is not critical, but is preferably less than room temperature (e.g., from xe2x88x9280 to xe2x88x9220 or even 0 degrees centigrade).
The compound of Formula IV above may be produced by reacting a compound of Formula III: 
wherein X is halogen, with sodium tert-butylthiolate or potassium tert-buthylthiolate to produce a compound of Formula IV. This reacting step may be carried out in any suitable solvent, preferably nonaqueous, such as a polar aprotic solvent (e.g., dimethylformamide and/or dimethylsulfoxide). The reacting step may be carried out at any suitable temperature, such as from 20 to 120 or 130 degrees centigrade. Compounds of Formula III are known or may be prepared in accordance with known techniques.
The present invention is explained in greater detail in the following non-limiting examples.